A photo-thermal and coal-fired unit coupling system and a control method thereof

Abstract

The present application relates to the technical field of steam boiler, disclose a kind of photo-thermal and coal-fired unit coupling system and its control method, comprising: solar module and high-temperature heat pump module and molten salt heat storage module and coal power coupling module connected in sequence;Solar module includes solar light condensing and heat collecting unit and solar steam generating unit, output steam is transported to high-temperature heat pump module by energy transport module;High-temperature heat pump module includes steam-air heat exchanger and molten salt-air heat exchanger, steam enters high-temperature heat pump module by steam-air heat exchanger, and then is transported to molten salt heat storage module by molten salt steam heat exchanger;Molten salt heat storage module is connected with coal power coupling module by its internal molten salt heat storage steam generating unit, and the superheated steam generated by it is connected with coal-fired boiler main steam pipeline.Solve the problem of low thermal efficiency, poor peak shaving flexibility and large energy transmission loss in the prior art, achieve the purpose of efficient energy conversion, reduce coal consumption and small energy transmission loss.

Description

Technical Field

[0001] This invention relates to the field of steam boiler technology, and in particular to a solar thermal and coal-fired power unit coupling system and its control method. Background Technology

[0002] Deeply coupling concentrated solar power (CSP) with coal-fired power generation creates a solar-coal hybrid power system. This system not only utilizes the turbine power generation portion of the coal-fired generator unit to reduce costs but also decreases coal consumption, achieving cleaner power generation from coal-fired units. In existing technologies, the integration of solar thermal power with the coal-fired unit is located on the regenerative system side or replaces part of the boiler reheater. This involves using solar thermal energy to replace regenerative extraction steam to heat boiler feedwater or reheat steam. This integration method has low system thermal economy and does not align with energy development goals. Furthermore, existing technologies require limitations on the form of solar concentrators, the solar thermal heat transfer medium, and the parameter levels of the coal-fired unit, lacking scalability and versatility.

[0003] For example, Chinese patent CN108731286A discloses a solar thermal molten salt thermal storage and solar-coal coupling system and method, providing the following technical solution: a solar thermal molten salt thermal storage device; the solar thermal molten salt thermal storage device includes a solar thermal collector, a molten salt storage tank, and a molten salt heat exchanger. The solar thermal collector transfers heat to the molten salt storage tank, and the molten salt storage tank provides heat energy to the thermal system of a thermal power plant through the molten salt heat exchanger, or conversely, obtains heat from the extraction steam system of the thermal power plant for molten salt thermal storage. In this invention, the solar thermal molten salt thermal storage system exchanges heat with the thermal power plant through the molten salt exchanger, realizing solar-coal coupling. This can effectively utilize solar thermal resources, save energy, and can assist in heating and power generation during peak heat demand periods at thermal power plants. Conversely, it can store excess heat energy from thermal power plants in molten salt and supply it to the thermal power plant during peak heat demand periods, thereby achieving thermal power plant peak shaving and frequency regulation. However, the aforementioned solar thermal molten salt thermal storage solar coal coupling system and method only couples with the thermal power plant through direct heat exchange with molten salt. It lacks energy enhancement means such as high-temperature heat pumps, cannot efficiently convert low-quality heat energy, has limited peak-shaving capacity, and cannot compensate for transmission losses when transporting steam over long distances, resulting in a significant reduction in transmitted energy. This leads to low system thermal economy and limited applicability. Summary of the Invention

[0004] This invention solves the problems of low thermal economy, poor peak-shaving flexibility, insufficient coupling versatility, and large energy transmission loss in the prior art. It proposes a solar thermal and coal-fired unit coupling system and its control method, which achieves the goals of high-efficiency energy conversion, flexible peak-shaving and frequency regulation, reduced coal consumption, and low energy transmission loss.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A solar thermal and coal-fired power unit coupling system includes: a solar energy module, a high-temperature heat pump module, a molten salt thermal storage module, and a coal-fired power coupling module connected in sequence; The solar module includes a solar concentrating and collecting unit and a solar steam generating unit. The output steam is delivered to the high-temperature heat pump module through the energy transmission module. The high-temperature heat pump module includes a steam-air heat exchanger and a molten salt-air heat exchanger. Steam enters the high-temperature heat pump module through the steam-air heat exchanger and is then transported to the molten salt heat storage module through the molten salt steam heat exchanger. The molten salt thermal storage module is connected to the coal-fired power coupling module through its internal molten salt thermal steam generation unit, and the superheated steam it generates is connected to the main steam pipeline of the coal-fired boiler.

[0006] This system achieves deep coupling of solar thermal and coal-fired power generation. By utilizing the existing steam turbine power generation section of coal-fired units, construction costs are significantly reduced. Simultaneously, by replacing part of the coal with solar thermal energy, coal consumption is reduced, achieving the goal of clean power generation. The system design does not restrict the form of solar concentrator and the choice of heat transfer medium, such as tower, trough, or molten salt, making it widely applicable and flexibly adaptable to coal-fired units with various parameter levels, thereby improving overall energy utilization efficiency.

[0007] A method for coupled control of solar thermal and coal-fired power units includes: The system detects light intensity and adjusts the mode according to the coal-fired unit load, the liquid level in the high-temperature molten salt tank, and the liquid level in the low-temperature molten salt tank: real-time power generation mode, solar thermal energy storage mode, coal-fired peak shaving mode, or energy storage power generation mode. Based on the temperature and pressure values ​​at key points in the steam and condensate pipes, if the difference between the temperature and pressure values ​​and the starting point is greater than the preset value, the corresponding photovoltaic electric heater module will be activated to supplement the pressure until the difference between the temperature and pressure values ​​and the starting point is lower than the preset value. Based on the inlet steam parameters of the high-temperature heat pump module and the target temperature of the molten salt, the compressor speed and expander guide vane opening are optimized in real time.

[0008] The system dynamically optimizes operation based on real-time data, prioritizing power generation or energy storage during periods of abundant sunshine, and peak shaving or energy storage-based power generation during periods of insufficient sunshine, maximizing the utilization of renewable energy. The photovoltaic electric heater intelligently compensates for pipeline losses, and the compressor speed is optimized to match the molten salt temperature, improving energy efficiency, reducing curtailment, and enhancing system stability and environmental friendliness.

[0009] Preferably, the solar module further includes a heat transfer medium circulation pump, and the solar steam generating unit includes a first preheater, a first evaporator, and a first superheater. The high-temperature heat transfer medium passes sequentially through the working medium side of the first superheater, the first evaporator, and the first preheater, and is cooled to a low-temperature heat transfer medium. After passing through the heat transfer medium circulation pump, it enters the solar concentrating heat collection system to absorb heat.

[0010] This system achieves efficient recycling of the heat transfer medium, maximizing solar heat absorption and improving steam generation efficiency through multi-stage heat exchange via preheaters, evaporators, and superheaters. The circulating pump ensures stable system operation, adapting to various environmental conditions, such as the low temperatures and high wind speeds of desert regions, reducing heat loss and improving the economic efficiency and reliability of solar thermal projects.

[0011] Preferably, the high-temperature heat pump module also includes an air compressor and an air expander. Air flows sequentially through a steam-air heat exchanger and an air compressor, and then through a molten salt air heat exchanger and an air expander to form a closed loop. The outlet temperature of the air compressor is adjusted by the number of compressor stages to match the main steam parameters of the coal-fired unit. The molten salt air heat exchanger cools the air to medium-temperature, high-pressure air while heating the molten salt. The air expander recovers energy and reduces the air parameters.

[0012] Utilizing direct-drive with green electricity, it consumes no additional fossil fuels, resulting in high energy efficiency. Compatibility is enhanced by adjusting the compressor stages to match the main steam parameters of coal-fired units, such as subcritical or supercritical units. An air expander recovers energy, reducing parameters and minimizing waste, while molten salt heating stores heat, supporting multiple operating modes and enhancing system flexibility.

[0013] Preferably, the molten salt thermal storage module further includes a high-temperature molten salt tank and a low-temperature molten salt tank. The molten salt in the low-temperature molten salt tank is pumped into a molten salt air heat exchanger and heated to high-temperature molten salt before entering the high-temperature molten salt tank for storage or directly entering the molten salt thermal storage steam generation unit. The molten salt thermal storage steam generation unit includes a second preheater, a second evaporator, and a second superheater. The molten salt flows through the second superheater, the second evaporator, and the working fluid side of the second preheater to cool down to low-temperature molten salt before entering the low-temperature molten salt tank.

[0014] It achieves efficient heat storage and on-demand release, supporting multiple modes such as real-time power generation, energy storage, and peak shaving through the combination of high-temperature and low-temperature molten salt tanks. The molten salt pump and steam generation system ensure stable heat exchange, heating the molten salt to generate high-temperature steam, which is directly used for power generation, improving system response speed and economy, and reducing energy waste.

[0015] Preferably, the feedwater from the coal-electric coupling module passes sequentially through the water side of the second preheater, the second evaporator, and the second superheater, becoming superheated steam before entering the coal-electric coupling module. The condensate from the energy transmission module passes sequentially through the water side of the first superheater, the first evaporator, and the first preheater, becoming superheated steam before entering the energy transmission module.

[0016] Multi-stage preheating and superheating enhance steam parameters, reducing energy loss during transmission. Condensate recycling improves water resource efficiency, ensuring the system maintains high thermal economy even under long pipeline transport, thus reducing operating costs.

[0017] Preferably, the energy transmission module includes a steam pipe and a condensate pipe with a length of less than or equal to 50 km. A photovoltaic electric heater module is installed at a key point of the steam pipe and the condensate pipe. The photovoltaic electric heater module is equipped with a temperature and pressure sensor and a photovoltaic module. The steam DC electric heater and the condensate DC electric heater are respectively connected to the photovoltaic module through a circuit breaker.

[0018] To address the heat loss problem in long pipelines, a photovoltaic DC-powered heater is used to compensate for temperature rise in real time, and steam supplementation heating is provided at key points. This significantly improves energy transmission efficiency and reduces temperature fluctuations. It also enhances the system's adaptability to harsh environments such as deserts and wastelands, ensuring stable operation and reducing operating costs.

[0019] Preferably, the coal-fired power coupling module includes a coal-fired boiler, a high-pressure heater, and a feedwater pump; the coal-fired boiler is also connected to a high-pressure cylinder and an intermediate-pressure cylinder, and the intermediate-pressure cylinder is also connected to a low-pressure cylinder; the steam extraction pipe of the intermediate-pressure cylinder is connected to the steam pipe of the energy transmission module, and the steam is transported to the high-temperature heat pump module for heat storage through the energy transmission module; the condensate after the steam passes through the steam-air heat exchanger is pumped into the deaerator by the condensate pump; the deaerator and the high-pressure heater are connected through the feedwater pump.

[0020] Utilizing steam extracted from the intermediate-pressure cylinder for heat storage reduces the output of coal-fired units, thus aiding in peak shaving for the power grid. Drainage is recovered to the deaerator to improve system closed-loop efficiency and reduce water waste. High-pressure heaters and feedwater pumps ensure stable feedwater parameters, enhancing overall system reliability and energy return efficiency.

[0021] Preferably, the superheated steam generated by the molten salt thermal storage module is directly connected to the main steam pipeline at the outlet of the coal-fired boiler and enters the high-pressure cylinder of the turbine to generate electricity. The outlet of the high-pressure heater supplies feedwater to the second preheater of the molten salt thermal storage module. The molten salt thermal storage module and the coal-electric coupling module are equipped with a valve control system, including several bypass valves and several flow control valves, so that the high-temperature molten salt can directly enter the steam generation system or be stored in the high-temperature molten salt tank, realizing the physical switching of various modes.

[0022] It enables flexible switching of operating modes, adjusting the molten salt path through bypass and flow control valves to adapt to different lighting and load conditions. Direct connection to the main steam pipeline ensures efficient power generation, reduces heat loss, improves system adaptability and economy, and meets the dynamic needs of the power grid.

[0023] Preferably, the adjustment mode includes: if the solar radiation level is greater than the light threshold and the coal-fired unit load is lower than the load threshold, the solar heat is stored in molten salt through the high-temperature heat pump module; otherwise, the solar module is controlled to generate superheated steam, which is then transported to the high-temperature heat pump module for power generation by the coal-electric coupling module. If the solar radiation level is not greater than the light threshold, when the coal-fired unit load is higher than the load threshold, if the high-temperature molten salt tank level is low and the low-temperature molten salt tank level is high, steam is extracted from the intermediate-pressure cylinder and stored as heat through the energy transmission module and the high-temperature heat pump module. If the high-temperature molten salt tank level is high and the low-temperature molten salt tank level is low, superheated steam is generated by the molten salt heat storage module to assist the coal-electric coupling module in power generation.

[0024] To ensure efficient system operation under various conditions, thermal energy storage prevents solar curtailment during low load periods and power generation or peak shaving during high load periods, thereby improving energy utilization. Utilizing low-quality steam thermal energy storage to generate high-quality steam for power generation results in high energy return efficiency and enhances grid compatibility.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows.

[0026] 1. This invention involves distributing temperature and pressure sensors along the steam and condensate pipelines of the energy transmission module, and installing photovoltaic modules and DC electric heaters near the midpoint to achieve real-time monitoring and intelligent compensation. The start and stop of the electric heaters are controlled by a circuit breaker to ensure that the difference between the working fluid parameters and the starting point is below a preset value. This design directly addresses the high heat loss problem in long-distance transportation or harsh environments such as deserts and wastelands. Utilizing direct photovoltaic DC power supply avoids inverter losses, effectively reducing energy attenuation during transmission and maintaining stable system operation. Simultaneously, the introduction of the photovoltaic electric heater module not only reduces pipeline insulation costs but also improves overall thermal economy, enabling the system to maintain efficient energy transfer over long distances, providing feasible support for the off-site construction of solar thermal and coal-fired projects.

[0027] 2. The high-temperature heat pump module of this invention achieves efficient conversion and enhancement of low-quality heat energy. Driven directly by green electricity, it forms a closed loop through a steam-air heat exchanger, an air compressor, a molten salt-air heat exchanger, and an air expander. This converts the low-temperature steam input from the solar module into high-temperature, high-pressure air, which then heats the molten salt. The outlet temperature of the air compressor can be adjusted in stages to match the main steam parameters of the coal-fired unit, ensuring system compatibility. Furthermore, extreme value search control dynamically optimizes the operating parameters of the compressor and expander, achieving intelligent conversion of low-quality heat energy into high-quality heat energy, thus significantly improving system energy efficiency.

[0028] 3. This invention significantly reduces power generation costs and coal consumption through deep coupling of solar thermal and coal-fired power units, achieving clean power generation; it boasts higher thermal economics and is not limited by solar concentrating methods or heat transfer media, exhibiting strong versatility. The system supports multiple operating modes, including real-time power generation, solar thermal energy storage, coal-fired peak shaving, and energy storage power generation, enhancing flexibility and efficiency with high energy return efficiency. Attached Figure Description

[0029] Figure 1 This is a system block diagram of a real-time power generation mode of a solar thermal and coal-fired power unit coupling system and its control method according to the present invention.

[0030] Figure 2 This is a block diagram of a solar thermal energy storage mode system for a solar thermal and coal-fired power unit coupling system and its control method according to the present invention.

[0031] Figure 3 This is a system block diagram of an energy storage power generation mode of a solar thermal and coal-fired power unit coupling system and its control method according to the present invention.

[0032] Figure 4 This is a block diagram of a coal-fired peak-shaving mode system for a solar thermal and coal-fired power unit coupling system and its control method according to the present invention.

[0033] Figure 5 This is a block diagram of a photovoltaic electric heater module of a solar thermal and coal-fired power unit coupling system and its control method according to the present invention.

[0034] Illustration: 1. Solar concentrator unit; 2. Heat transfer fluid circulation pump; 3. First superheater; 4. First evaporator; 5. First preheater; 6. Condensate transfer pump; 7. Photovoltaic electric heater module; 8. Steam-air heat exchanger; 9. Air compressor; 10. Air expander; 11. Molten salt-air heat exchanger; 12. Low-temperature molten salt pump; 13. Low-temperature molten salt tank; 14. High-temperature molten salt pump; 15. High-temperature molten salt tank; 16. Second superheater; 17. Second evaporator; 18. Second preheater; 19. Drain pump; 20. Coal-fired boiler; 21. High-pressure heater; 22. Feed water pump; 23. Deaerator; 24. High-pressure cylinder; 25. Medium-pressure cylinder; 26. Low-pressure cylinder; 27. Photovoltaic module; 28. DC combiner box; 29. ​​Temperature and pressure sensor; 30. Steam DC electric heater; 31. Condensate DC electric heater; 32. First circuit breaker; 33. Second circuit breaker; 34. Third circuit breaker. Detailed Implementation

[0035] See Figures 1-5 As shown, a solar thermal and coal-fired power unit coupling system includes: a solar energy module, a high-temperature heat pump module, a molten salt thermal storage module, and a coal-fired power coupling module connected in sequence. The solar module includes a solar concentrating and collecting unit and a solar steam generating unit. The output steam is delivered to the high-temperature heat pump module through the energy transmission module. The high-temperature heat pump module includes a steam-air heat exchanger and a molten salt-air heat exchanger. Steam enters the high-temperature heat pump module through the steam-air heat exchanger and is then transported to the molten salt heat storage module through the molten salt steam heat exchanger. The molten salt thermal storage module is connected to the coal-fired power coupling module through its internal molten salt thermal steam generation unit, and the superheated steam it generates is connected to the main steam pipeline of the coal-fired boiler.

[0036] A method for coupled control of solar thermal and coal-fired power units includes: The system detects light intensity and adjusts the mode according to the coal-fired unit load, the liquid level in the high-temperature molten salt tank, and the liquid level in the low-temperature molten salt tank: real-time power generation mode, solar thermal energy storage mode, coal-fired peak shaving mode, or energy storage power generation mode. Based on the temperature and pressure values ​​at key points in the steam and condensate pipes, if the difference between the temperature and pressure values ​​and the starting point is greater than the preset value, the corresponding photovoltaic electric heater module will be activated to supplement the pressure until the difference between the temperature and pressure values ​​and the starting point is lower than the preset value. Based on the inlet steam parameters of the high-temperature heat pump module and the target temperature of the molten salt, the compressor speed and expander guide vane opening are optimized in real time.

[0037] like Figures 1-4 In one embodiment shown, Figure 1 This is an overall flowchart of a multi-event fusion scheduling method for emergency tasks in rail transit according to the present invention. Figure 2 This is a block diagram of a solar thermal energy storage system, which is a coupled solar thermal and coal-fired power unit system and its control method according to the present invention. Figure 3 This is a system block diagram of an energy storage power generation mode of a solar thermal and coal-fired power unit coupling system and its control method according to the present invention. Figure 4 This is a block diagram of a coal-fired peak-shaving mode system for a solar thermal and coal-fired power unit coupling system and its control method according to the present invention. This system is not limited to the form of solar concentrating collectors and can employ various types of solar concentrating collectors, such as tower, trough, linear Fresnel, and disc types. The solar module includes a solar concentrating collector system, a heat transfer fluid circulation pump, and a solar module steam generation system. The solar module steam generation system includes a preheater, an evaporator, and a superheater. The high-temperature heat transfer fluid sequentially passes through the superheater, evaporator, and preheater, cooling to a low-temperature heat transfer fluid, which then enters the solar concentrating collector system to absorb heat energy after passing through the heat transfer fluid circulation pump. Condensate from the energy transfer module sequentially passes through the superheater, evaporator, and preheater, becoming superheated steam, which then enters the energy transfer module. The present invention is not limited to the selection of the heat transfer fluid and can employ various types of working fluids, such as water / steam, thermal oil, molten salt, and air. This invention can be adapted to various concentrating heat collection forms and heat transfer media and coupled with coal-fired power units of various parameter levels, thus having a wider range of applications.

[0038] Energy transfer module: This includes related pipelines, with steam pipeline length L ≤ 50km. The energy transfer module is primarily responsible for transferring energy from the solar energy module and the high-temperature heat pump module. The relatively long pipeline length of the energy transfer module, coupled with the fact that solar thermal project sites are typically located in barren or desert areas characterized by low temperatures and high wind speeds, ultimately leads to significant heat loss in the energy transfer module pipelines. Figure 5 As shown, Figure 5 This is a block diagram of a photovoltaic electric heater module in a solar thermal and coal-fired power unit coupling system and its control method according to the present invention. Temperature and pressure sensors are distributed along the steam and condensate pipelines to monitor the working fluid parameters in real time. Near the midpoint between the solar thermal and coal-fired power projects, photovoltaic modules, a DC combiner box, a circuit breaker, a steam DC electric heater, and a condensate DC electric heater are centrally located. This invention does not include an inverter; the photovoltaic DC power supply directly powers the heaters.

[0039] The specific calculation of photovoltaic module design capacity is as follows: The design capacity equals the estimated steam capacity plus the estimated condensate capacity. The estimated steam capacity equals the rated steam flow rate multiplied by the steam specific heat capacity and then by the steam heating temperature rise T1. The estimated condensate capacity equals the rated condensate flow rate multiplied by the condensate specific heat capacity and then by the condensate heating temperature rise T2. The selection of the steam heating temperature rise and the condensate heating temperature rise depends on the pipeline length.

[0040] In this embodiment, if the pipeline length is 20km, the steam heating temperature rise should be set to 20℃, and the condensate heating temperature rise should be set to 10℃.

[0041] The control of the first circuit breaker, the second circuit breaker, and the third circuit breaker is as follows: First circuit breaker: When the energy transmission module is operating normally, it is in the closed state; when the energy transmission module is not operating, it is in the open state. Second circuit breaker: When the energy transmission module is operating normally, if the temperature difference between the downstream temperature of the steam DC electric heater and the starting point of the steam pipeline (near the solar module) is lower than T1, it is in the closed state; when the temperature difference reaches or exceeds T1, it is in the open state. Second circuit breaker: When the energy transmission module is operating normally, if the temperature difference between the downstream temperature of the condensate DC electric heater and the starting point of the condensate pipeline (near the high-temperature heat pump module) is lower than T2, it is in the closed state; when the temperature difference reaches or exceeds T2, it is in the open state.

[0042] The high-temperature heat pump module comprises a steam-air heat exchanger, an air compressor, an air expander, and a molten salt air heat exchanger. Air sequentially passes through the steam-air heat exchanger, air compressor, molten salt air heat exchanger, and air expander before re-entering the steam-air heat exchanger, forming a cycle. The high-temperature heat pump module is driven by direct green electricity connection, meaning that renewable energy sources such as wind and solar power are not directly connected to the public power grid but are supplied with green electricity through a direct connection line. Simultaneously, based on the inlet steam parameters and the target molten salt temperature of the high-temperature heat pump module, the system optimizes the compressor speed and expander guide vane opening in real time.

[0043] In this invention, the core components of the high-temperature heat pump module include a steam-air heat exchanger, an air compressor, a molten salt air heat exchanger, and an air expander. The real-time optimization objective is to dynamically adjust the compressor speed and expander guide vane opening based on inlet steam parameters (pressure, temperature) and the target molten salt temperature to maximize heat pump efficiency or minimize energy loss. The specific implementation steps are as follows: In this embodiment, the performance index COP, which is the ratio of output heat to input electrical power, serves as the core control target parameter for the energy-efficient operation of the high-temperature heat pump module. The molten salt heat exchange can be calculated by the temperature change of the molten salt air heat exchanger, and the green electricity input power comes from directly connected wind power or photovoltaic power.

[0044] Specific parameters are input. The inlet steam parameters of the high-temperature heat pump module are monitored in real time by temperature and pressure sensors on the steam pipeline, including steam pressure and temperature. These parameters affect the heat exchange efficiency of the steam-air heat exchanger. The target temperature of molten salt is set according to the operating mode. For example, in the real-time power generation mode in this embodiment, the target temperature of molten salt is 565°C. The actual molten salt temperature is obtained by the sensor of the molten salt thermal storage module.

[0045] Separate regulation loops are designed for the compressor and expander to optimize the compressor speed and expander guide vane opening respectively. In this embodiment, compressor speed optimization first controls the compressor speed by superimposing a sinusoidal disturbance onto the speed setpoint, measuring the change in COP, obtaining a gradient signal by high-pass filtering and multiplying it with the disturbance signal, and then using integral adjustment to update the speed setpoint to maximize COP. The specific adjustment method is dw. c / dt equals k c Multiply by the gradient estimate, w c k is the compressor speed. c To achieve integral gain, the optimization objective is to match the compressor outlet air temperature with the molten salt heating requirements while reducing green electricity consumption. In another embodiment, compressor speed regulation optimization specifically involves changing the power supply frequency input to the compressor via a frequency converter, thereby adjusting the motor speed. The compressor speed is automatically corrected using the compressor outlet temperature and COP value as feedback signals. In this embodiment, if the compressor outlet temperature is higher than the target value, the frequency is reduced by 5Hz each time; if the COP value is lower than the threshold, the minimum speed of 30Hz is locked to avoid inefficient operation. The maximum speed is set to not exceed 1.1 times the motor's rated speed, and the minimum speed is set to not be lower than 30Hz.

[0046] In this embodiment, the expansion vane opening optimization specifically involves first controlling the expansion vane opening to affect air expansion efficiency and energy recovery. Similarly, a disturbance is injected into the guide vane opening setpoint, the COP response is monitored, and the guide vane opening is adjusted to maximize energy recovery and ensure stable air parameter circulation.

[0047] In another embodiment, the expansion vane opening optimization specifically involves synergistically improving the system's COP to avoid energy waste caused by a mismatch between the vane opening and the load. The vane opening is dynamically adjusted based on the compressor outlet temperature deviation as the core signal. In this embodiment, if the compressor outlet temperature is lower than the target value (deviation > 2°C), the vane opening is increased by 5-8%, increasing the working fluid flow; if it is higher than the target value (deviation > 2°C), the opening is decreased by 3-5%, reducing the working fluid flow. Each adjustment does not exceed 8%, with a 30-second interval to avoid sudden changes in opening causing system oscillations. A minimum opening of 10% is set (to prevent jamming), and a maximum opening of 85% is set (to prevent excessive flow leading to a sudden pressure drop).

[0048] Furthermore, since the compressor speed and guide vane opening are coupled, time-sharing disturbance or multivariable control algorithms can be used to avoid interference. In this embodiment, when the compressor frequency increases (frequency + 5Hz), the guide vane opening increases synchronously by 3-5% to match the working fluid demand in advance. When the compressor frequency decreases (frequency - 5Hz), the guide vane opening decreases by 2-3% with a 10-second lag to avoid pressure fluctuations caused by a sudden decrease in flow.

[0049] In terms of the overall process, the target temperature of molten salt and initial control parameters are first set, the inlet steam parameters and molten salt temperature are continuously monitored, the control cycle is optimized, disturbances are injected, the gradient of COP is calculated, the compressor speed and expander guide vane opening are adjusted, and the COP is verified to see if it is improved; otherwise, the gain parameters are adjusted.

[0050] Molten salt thermal energy storage module: Includes a high-temperature molten salt tank, a low-temperature molten salt tank, a high-temperature molten salt pump, a low-temperature molten salt pump, and a steam generation system for the molten salt thermal energy storage module. Molten salt in the low-temperature molten salt tank is pumped by the low-temperature molten salt pump into the molten salt-air heat exchanger of the high-temperature heat pump module, where it is heated to become high-temperature molten salt and enters the high-temperature molten salt tank. Molten salt in the high-temperature molten salt tank is pumped by the high-temperature molten salt pump into the steam generation system. The steam generation system for the molten salt thermal energy storage module includes a preheater, an evaporator, and a superheater. Molten salt sequentially passes through the working fluid side of the superheater, evaporator, and preheater, cooling to low-temperature molten salt before entering the low-temperature molten salt tank. Feedwater from the coal-fired power generation module sequentially passes through the water side of the preheater, the evaporator, and the superheater, becoming superheated steam that enters the coal-fired power generation module.

[0051] The coal-fired power coupling module includes a coal-fired boiler, high-pressure cylinder, intermediate-pressure cylinder, low-pressure cylinder, high-pressure heater, and feedwater pump. Superheated steam from the molten salt thermal storage module is connected to the main steam pipeline at the coal-fired boiler outlet. A pipeline extends from the feedwater pipeline at the high-pressure heater outlet to the molten salt thermal storage module. The steam extraction pipelines of the turbine's third or fourth stage (i.e., the intermediate-pressure cylinder extraction pipeline) are connected to the steam pipelines of the energy transmission module.

[0052] This invention also relates to a method for coupled control of solar thermal and coal-fired power units, which can achieve the following functions: Real-time power generation mode: such as Figure 1 As shown, Figure 1 This is a system block diagram of a real-time power generation mode for a solar thermal and coal-fired power unit coupling system and its control method according to the present invention. Within the solar module, a low-temperature heat transfer medium absorbs heat energy after entering the solar concentrating collector system. A high-temperature heat transfer medium then sequentially passes through the working fluid side of the superheater, evaporator, and preheater, heating the condensate from the energy transfer module into superheated steam. The parameters of the superheated steam produced within the solar module directly affect the construction cost of the energy transfer module and the operating cost of the high-temperature heat pump module. Lower steam parameters result in lower construction costs for the energy transfer module, but increase the operating cost of the high-temperature heat pump module. The optimal parameters obtained after optimization are 1.5~2.5 MPa and 250~350℃. The superheated steam is transported to the high-temperature heat pump module through the energy transfer module. The length of the steam pipeline mainly affects the energy loss during energy transfer. Due to different site selection principles, solar thermal projects and coal-fired projects cannot be constructed at the same site; therefore, a steam pipeline length L ≤ 50 km is recommended.

[0053] Within the high-temperature heat pump module, superheated steam serves as the low-temperature heat source. Through a steam-air heat exchanger within the module, low-temperature, low-pressure air is heated to medium-temperature, low-pressure air with parameters of ~1.5 MPa and ~200℃. This medium-temperature, low-pressure air then passes through an air compressor, where it is compressed into high-temperature, high-pressure air with parameters of 3.0~5.5 MPa and 580~650℃. The air compressor outlet parameters primarily depend on the main steam parameters of the coal-fired unit. For subcritical coal-fired units, the air compressor outlet temperature is ~580℃; for supercritical coal-fired units, it is ~650℃. The air compressor outlet temperature can be adjusted by the number of compressor stages; higher stages result in higher outlet temperatures. The high-temperature, high-pressure air then passes through a molten salt air heat exchanger within the module, where it is cooled to medium-temperature, high-pressure air, and the molten salt is heated to 550~620℃. Finally, the medium-temperature, high-pressure air passes through an air expander to recover energy, becoming low-temperature, low-pressure air.

[0054] Within the molten salt thermal storage module, high-temperature molten salt directly enters the steam generation system. The molten salt sequentially passes through the working fluid side of the superheater, evaporator, and preheater, heating the feedwater from the coal-power coupling module into superheated steam. The superheated steam has a temperature range of 540~610℃, allowing coupling with coal-fired units of various parameter types. Within the coal-power coupling module, the superheated steam from the molten salt thermal storage module is connected to the main steam pipeline at the outlet of the coal-fired boiler, directly entering the turbine for power generation. A pipeline extends from the feedwater pipeline at the outlet of the high-pressure heater to the molten salt thermal storage module.

[0055] Solar thermal energy storage mode: such as Figure 2 As shown, Figure 2 This is a block diagram of a solar thermal energy storage mode system for a solar thermal and coal-fired power unit coupling system and its control method according to the present invention. Figure 1 In contrast, the coal-fired thermal storage module in this diagram does not interact with the coal-fired power coupling module. The coal-fired unit operates independently, storing the heat generated by solar and thermal processes. Figure 1 In the process, after the molten salt in the low-temperature molten salt tank is heated, it passes through the bypass of the high-temperature molten salt tank and directly enters the steam generation system. Figure 2 In the process, the molten salt in the low-temperature molten salt tank is heated and then directly enters the high-temperature molten salt tank for storage. This is controlled by valves within the molten salt thermal storage module. Superheated steam from the solar module transfers heat to the molten salt via a high-temperature heat pump module. Within the molten salt thermal storage module, the high-temperature molten salt directly enters the high-temperature molten salt tank for storage. The low-temperature molten salt in the low-temperature molten salt tank is pressurized by a low-temperature molten salt pump and then enters the molten salt-air heat exchanger to absorb heat.

[0056] Coal-fired peak-shaving mode: such as Figure 3 As shown, Figure 3 This is a system block diagram of an energy storage power generation mode of a solar thermal and coal-fired power unit coupling system and its control method according to the present invention.Figure 1 In contrast, in this diagram, the molten salt energy storage module only outputs heat. The hot molten salt from the high-temperature molten salt tank returns to the low-temperature molten salt tank. This is controlled by valves within the molten salt thermal storage module. Steam is generated and sent to the turbine for power generation. The turbine's third or fourth stage extraction steam pipe (i.e., the intermediate-pressure cylinder extraction steam pipe) is connected to the energy transfer module's steam pipe. When the coal-fired unit needs peak shaving, the turbine steam is drawn out and enters the energy transfer module. The steam, after passing through the steam-air heat exchanger, generates condensate, which is then pumped into the deaerator by a condensate pump. The intermediate-pressure cylinder outlet steam transfers heat to the molten salt via the high-temperature heat pump module. Within the molten salt thermal storage module, the high-temperature molten salt directly enters the high-temperature molten salt tank for storage.

[0057] Compared to other coal-fired power generation coupled with molten salt peak shaving schemes, the advantage of this peak shaving mode lies in its ability to utilize low-quality steam for energy storage and generate high-quality steam for power generation. The energy round-trip efficiency can reach over 60%.

[0058] Energy storage power generation mode: such as Figure 4 As shown, Figure 4 This is a block diagram of a coal-fired peak-shaving mode system for a solar thermal and coal-fired power unit coupling system and its control method according to the present invention. Figure 2 The only difference is that the valves on the steam pipeline from the intermediate-pressure cylinder outlet to the energy transmission module and the valve at the outlet of the condensate pump are open. This extracts steam from the intermediate-pressure cylinder outlet to aid in peak-shaving operation of the unit. Within the coal-power coupling module, superheated steam from the molten salt thermal storage module is connected to the main steam pipeline at the coal-fired boiler outlet and directly enters the turbine for power generation. A pipeline is connected from the feedwater pipeline at the high-pressure heater outlet to the molten salt thermal storage module. Inside the molten salt thermal storage module, feedwater is heated into superheated steam through the module's steam generation system.

[0059] The specific control strategy is as follows: Solar thermal energy, as a typical renewable energy source, is affected by various natural factors such as sunshine duration, radiation intensity, and weather conditions, exhibiting significant intermittency and fluctuation.

[0060] When sunlight conditions are favorable and the coal-fired unit is under high load, the system switches to real-time solar power generation mode. In this mode, solar thermal energy directly generates steam to assist the coal-fired unit in peak power generation. This is independent of the molten salt tank level.

[0061] When sunlight conditions are good and the coal-fired unit load is low, if the high-temperature molten salt tank level is low and the low-temperature molten salt tank level is high, the system should switch to solar thermal energy storage mode. In this mode, the solar energy is stored in the molten salt. If the high-temperature molten salt tank level is high and the low-temperature molten salt tank level is low, the molten salt tanks cannot store more heat, and solar energy should be abandoned.

[0062] When lighting conditions are poor and the coal-fired unit is under high load, if the high-temperature molten salt tank level is low and the low-temperature molten salt tank level is high, there is no excess heat to store, and the coal-fired unit should operate independently. If the high-temperature molten salt tank level is high and the low-temperature molten salt tank level is low, the unit should switch to energy storage and power generation mode. In this mode, the heat stored in the molten salt will be used to assist the coal-fired unit in peak power generation.

[0063] When lighting conditions are poor and the coal-fired unit load is low, if the high-temperature molten salt tank level is low and the low-temperature molten salt tank level is high, the system should switch to coal-fired peak-shaving mode. In this mode, heat storage is achieved by extracting steam from the intermediate-pressure cylinder, and the output of the coal-fired unit can be reduced, thus assisting in peak-shaving operation. If the high-temperature molten salt tank level is high and the low-temperature molten salt tank level is low, the heat coupled to the coal-fired unit due to the low unit load will adversely affect the low-load operation of the coal-fired boiler. In this case, the coal-fired unit should operate independently.

[0064] The above only provides control strategies for a few typical operating conditions. In actual operation, these strategies can be flexibly switched according to the requirements of the power grid and potential benefits.

[0065] In one embodiment, a 300MW subcritical coal-fired power unit coupled with a thermal oil trough-type solar thermal power generation system is used as an example for real-time power generation. The length of the steam pipeline within the energy transmission module is L=20km. The solar mirror field area is considered to be 800,000m2.

[0066] Solar module: Cold heat transfer oil parameters 2.0MPa, 230℃. It enters the solar concentrator system via a heat transfer oil pump to absorb heat, becoming hot heat transfer oil with parameters 350℃. Condensate from the energy transfer module parameters 3.0MPa, 180℃, 290t / h passes sequentially through the water side of the superheater, evaporator, and preheater, becoming superheated steam with parameters 2.8MPa, 340℃.

[0067] Energy transfer module: The steam parameters on the high-temperature heat pump module side are 2.5MPa and 300℃. The condensate parameters on the high-temperature heat pump module side are 2.3MPa and 200℃, and the condensate is pumped to the solar module.

[0068] High-temperature heat pump module: The heat pump circulation medium is air. The air passes through a steam-air heat exchanger, where it is heated to 1.5 MPa and 200°C; after passing through an air compressor, the parameters are 5.0 MPa and 580°C; after passing through a molten salt air heat exchanger, the parameters are 4.8 MPa and 410°C; and after passing through an air expander, the parameters are 1.55 MPa and 190°C. The high-temperature heat pump module system has a COP of 1.4. The high-temperature heat pump module is driven by direct-drive green electricity, thus absorbing green electricity without consuming additional fossil fuels.

[0069] Molten salt thermal storage module: The molten salt in the low-temperature molten salt tank has a temperature of 350℃. It is then pumped into the molten salt-air heat exchanger and heated to a high-temperature molten salt temperature of 565℃. The high-temperature molten salt then enters the steam generation system. Feedwater from the coal-electricity coupling module has a feedwater temperature of 18MPa and 250℃. This feedwater passes sequentially through the water side of the preheater, the evaporator, and the superheater, becoming superheated steam with a temperature of 16.7MPa, 540℃, and a flow rate of 350t / h before entering the coal-electricity coupling module.

[0070] The coal-power coupling module generates electricity by supplying 16.7 MPa, 540℃, and 350 t / h of steam into the main steam pipe of the turbine, with an estimated output of 110 MW. Under full load conditions for coal-fired units, this can reduce coal consumption by 35%, demonstrating significant energy-saving and carbon-reduction effects.

Claims

1. A solar thermal and coal-fired power unit coupling system, characterized in that, include: The solar energy module, the high-temperature heat pump module, the molten salt thermal storage module, and the coal-fired power coupling module are connected in sequence. The solar module includes a solar concentrating and collecting unit (1) and a solar steam generating unit. The output steam is delivered to the high-temperature heat pump module through the energy transmission module. The high-temperature heat pump module includes a steam-air heat exchanger (8) and a molten salt air heat exchanger (11). Steam enters the high-temperature heat pump module through the steam-air heat exchanger (8) and is then transported to the molten salt heat storage module through the molten salt steam heat exchanger. The molten salt thermal storage module is connected to the coal-electric coupling module through its internal molten salt thermal steam generation unit, and the superheated steam generated by it is connected to the main steam pipeline of the coal-fired boiler (20).

2. The solar thermal and coal-fired power unit coupling system according to claim 1, characterized in that, The solar module also includes a heat transfer medium circulation pump (2). The solar steam generating unit includes a first preheater (5), a first evaporator (4), and a first superheater (3). The high-temperature heat transfer medium passes through the working medium side of the first superheater (3), the first evaporator (4), and the first preheater (5) in sequence, and is cooled to a low-temperature heat transfer medium. After passing through the heat transfer medium circulation pump (2), it enters the solar concentrating heat collection system to absorb heat.

3. A solar thermal and coal-fired power unit coupling system according to claim 1 or 2, characterized in that, The high-temperature heat pump module also includes an air compressor (9) and an air expander (10). Air flows through a steam-air heat exchanger (8) and an air compressor (9) in sequence, and then through a molten salt air heat exchanger (11) and an air expander (10) to form a closed loop. The outlet temperature of the air compressor (9) is adjusted by the number of compressor stages to match the main steam parameters of the coal-fired unit. The molten salt air heat exchanger (11) cools the air to medium-temperature high-pressure air while heating the molten salt. The air expander (10) recovers energy and reduces the air parameters.

4. The solar thermal and coal-fired power unit coupling system according to claim 3, characterized in that, The molten salt thermal storage module also includes a high-temperature molten salt tank (15) and a low-temperature molten salt tank (13). The molten salt in the low-temperature molten salt tank (13) is sent to the molten salt air heat exchanger (11) by the low-temperature molten salt pump (12) and heated to high-temperature molten salt before entering the high-temperature molten salt tank (15) for storage or directly entering the molten salt thermal storage steam generation unit. The molten salt thermal storage steam generation unit includes a second preheater (18), a second evaporator (17), and a second superheater (16). The molten salt flows through the working fluid side of the second superheater (16), the second evaporator (17), and the second preheater (18) to cool down to low-temperature molten salt before entering the low-temperature molten salt tank (13).

5. The solar thermal and coal-fired power unit coupling system according to claim 4, characterized in that, The feedwater from the coal-electric coupling module passes sequentially through the water side of the second preheater (18), the second evaporator (17), and the second superheater (16), and becomes superheated steam before entering the coal-electric coupling module. The condensate from the energy transmission module passes sequentially through the water side of the first superheater (3), the first evaporator (4), and the first preheater (5), and becomes superheated steam before entering the energy transmission module.

6. The solar thermal and coal-fired power unit coupling system according to claim 2, characterized in that, The energy transmission module includes a steam pipe and a condensate pipe with a length of less than or equal to 50 km. A photovoltaic electric heater module (7) is provided at the key points of the steam pipe and the condensate pipe. The photovoltaic electric heater module (7) is equipped with a temperature and pressure sensor (29) and a photovoltaic module (27). The steam DC electric heater (30) and the condensate DC electric heater (31) are respectively connected to the photovoltaic module (27) through a circuit breaker.

7. A solar thermal and coal-fired power unit coupling system according to claim 5 or 6, characterized in that, The coal-electric coupling module includes a coal-fired boiler (20), a high-pressure heater (21), and a feedwater pump (22); the coal-fired boiler (20) is also connected to a high-pressure cylinder (24) and a medium-pressure cylinder (25), and the medium-pressure cylinder (25) is also connected to a low-pressure cylinder (26); the extraction pipe of the medium-pressure cylinder (25) is connected to the steam pipe of the energy transmission module, and the steam is transported to the high-temperature heat pump module for heat storage through the energy transmission module; the condensate after the steam-air heat exchange is pumped into the deaerator (23) through the condensate pump (19); the deaerator (23) and the high-pressure heater (21) are connected through the feedwater pump (22).

8. The solar thermal and coal-fired power unit coupling system according to claim 7, characterized in that, The superheated steam generated by the molten salt thermal storage module is directly connected to the main steam pipeline at the outlet of the coal-fired boiler (20) and enters the high-pressure cylinder of the steam turbine to generate electricity. The outlet of the high-pressure heater (21) supplies feed water to the second preheater (18) of the molten salt thermal storage module. The molten salt thermal storage module and the coal-electric coupling module are equipped with a valve control system, including several bypass valves and several flow control valves, so that the high-temperature molten salt can directly enter the steam generation system or enter the high-temperature molten salt tank (15) for storage, realizing the physical switching of various modes.

9. A method for coupled control of a solar thermal and coal-fired power unit, employing the coupled solar thermal and coal-fired power unit system as described in any one of claims 1-8, characterized in that, include: Detect the light intensity and adjust the mode according to the coal-fired unit load and the liquid level of the high-temperature molten salt tank (15) and the liquid level of the low-temperature molten salt tank (13) to real-time power generation mode, solar thermal energy storage mode, coal-fired peak shaving mode or energy storage power generation mode. Based on the temperature and pressure values ​​at key points of the steam pipe and condensate pipe, if the difference between the temperature and pressure at the starting point is greater than the preset value, the corresponding photovoltaic electric heater module (7) will be activated to replenish until the difference between the temperature and pressure at the starting point is lower than the preset value. Based on the inlet steam parameters of the high-temperature heat pump module and the target temperature of the molten salt, the compressor speed and expander guide vane opening are optimized in real time.

10. The method for coupled control of solar thermal and coal-fired power units according to claim 9, characterized in that, include: The adjustment mode specifically includes: if the solar heat is greater than the light threshold and the load of the coal-fired unit is lower than the load threshold, the solar heat is stored in molten salt through the high-temperature heat pump module; otherwise, the solar module is controlled to generate superheated steam, which is then transported to the high-temperature heat pump module and generated by the coal-electric coupling module. If the light threshold is not greater than the light threshold, when the load of the coal-fired unit is higher than the load threshold, if the liquid level of the high-temperature molten salt tank (15) is low and the liquid level of the low-temperature molten salt tank (13) is high, steam is extracted from the intermediate pressure cylinder (25) and stored in the energy transmission module and the high-temperature heat pump module; if the liquid level of the high-temperature molten salt tank (15) is high and the liquid level of the low-temperature molten salt tank (13) is low, superheated steam is generated by the molten salt heat storage module to assist the coal-electric coupling module in generating electricity.

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